The present invention relates to an antiskid control system.
In conventional antiskid control systems, the down pressure timing of hydraulically operated brakes is determined by a first down pressure decision threshold with which detected wheel speed values are compared and by a second down pressure decision threshold with which wheel acceleration values are compared. With antiskid control systems of this type, the threshold values are estimated from the maximum wheel speed value and comparisons are made between the threshold values and wheel speeds and wheel accelerations to determine the optimum slip rate of the wheels. However, a difference in wheel diameter between wheels results in a false timing down-pressure operation. More specifically, if a given wheel has a lower tire pressure than the other wheels, the diameter of the given wheel is smaller than the others and its apparent wheel speed is greater than the speed of any other wheel and is taken as a maximum wheel speed. Thus, the estimated vehicle speed value is higher than is required for optimum operation of the brakes of the other wheels. Such situations may also occur in a vehicle running on a curved path. On a right-turn curve, for example, the front right wheel would turn at a speed lower than the front left wheel, so that the front right wheel speed becomes smaller than the front left wheel speed and it further reduces below a variable down pressure decision threshold. Down pressure operation thus occurs prematurely and the wheel brake pressure on a wheel following a smaller radius is excessively decreased in comparison with the fluid pressure on a wheel on the other end of the axle.